This invention relates to a self-locking telescoping device capable of functioning under impact as an energy absorber.
A motor vehicle typically includes a bumper bar and an energy absorber which supports the bumper bar on a body of the motor vehicle for translation though a relatively short energy-absorbing stroke in response to a low speed impact on the bumper bar. During the energy-absorbing stroke, a fraction of the kinetic energy of the impact is converted by the energy absorber into work. In a high speed impact on the bumper bar, however, its short energy-absorbing stroke is quickly traversed and most of the kinetic energy of the impact is converted into work by plastic deformation of body structure of the motor vehicle behind the bumper bar. As motor vehicles have become more compact, the energy-absorbing capability of their body structures has decreased due to the smaller span between the vehicle""s passenger compartment and bumper bar. A telescoping device described in U.S. Pat. No. 5,370,429 supports a bumper bar close to a body of a motor vehicle except when sensors on the vehicle detect an impending impact. Then, the telescoping device extends the bumper bar out from the body to maximize the energy-absorbing stroke of the bumper bar. During the energy-absorbing stroke, hydraulic fluid is throttled through an orifice of the telescoping device to absorb a fraction of the kinetic energy of the impact. The telescoping device described in the aforesaid U.S. Pat. No. 5,370,429 is not xe2x80x9cself-lockingxe2x80x9d, i.e., does not become structurally rigid in compression under any circumstances, and requires a fluid reservoir and fluid seals which may leak during the service life of the device. Accordingly, manufacturers continue to seek improved telescoping devices which are self-locking and which are also suitable for use as bumper energy absorbers.
This invention is a new and improved self-locking telescoping device including a stationary outer tube, an inner tube telescoped into the outer tube having a cone-shaped ramp at an inboard end thereof, and a plurality of metal spheres between the cone-shaped ramp and the outer tube. The metal spheres become wedged between the cone-shaped ramp and the outer tube when the inner tube is thrust into the outer tube in a collapse direction corresponding to a decrease in the length of the telescoping device thereby locking the inner and outer tubes together and rendering the telescoping device structurally rigid in the collapse direction. When the thrust is attributable to a severe impact on the inner tube, the spheres plastically deform the outer tube by plowing tracks therein thereby to convert into work a fraction of the kinetic energy of the impact. The self-locking telescoping device further includes an actuator rod, a driver which translates the actuator in the collapse direction and in an opposite expansion direction corresponding to an increase in the length of the telescoping device, a first clutch which translates the inner tube as a unit with the actuator rod in the expansion direction, a second clutch which translates the inner tube as a unit with the actuator rod in the collapse direction, and a tubular retainer on the actuator rod having a plurality of closed-ended slots around respective ones of the metal spheres. The ends of the slots prevent the spheres from becoming wedged between the cone-shaped ramp and the outer tube when the second clutch translates the inner tube as a unit with the actuator rod in the collapse direction.